Abstract
Insoluble fiber (IF) recovered from the enzyme-assisted aqueous extraction process (EAEP) of soybeans is a fraction rich in carbohydrates and proteins. It can be used to enhance ethanol production in an integrated corn-soy biorefinery, which combines EAEP with traditional corn-based ethanol processing. The present study evaluated IF as a substrate for ethanol production. The effects of treatment of IF (soaking in aqueous ammonia (SAA), liquid hot water (LHW), and enzymatic hydrolysis), primarily simultaneous saccharification and co-fermentation (SSCF), as well as scaling up (250 mL to 60 L) on ethanol production from IF alone or a corn and IF slurry were investigated. Enzymatic hydrolysis (pectinase, cellulase, and xylanase, each added at 5% soy solids during simultaneous saccharification and fermentation/SSCF) was the best treatment to maximize ethanol production from IF. Ethanol yield almost doubled when SSCF of IF was performed with Saccharomyces cerevisiae and Escherichia coli KO11. Addition of IF in dry-grind corn fermentation increased the ethanol production rate (~31%), but low ethanol tolerance of E. coli KO11 was a limiting factor for employing SSCF in combination corn and IF fermentation. Nonlinear Monod modeling accurately predicted the effect of ethanol concentration on E. coli KO11 growth kinetics by Hanes-Woolf linearization. Collectively, the results from this study suggest a potential of IF as a substrate, alone or in dry-grind corn fermentation, where it enhances the ethanol production rate. IF can be incorporated in the current bioethanol industry with no added capital investment, except enzymes.
Highlights
Enzyme-assisted aqueous extraction process (EAEP) is an environmentally friendly alternative to chemical or mechanical extraction of oil from soybeans [1,2,3].In comparison to conventional oil extraction methods, EAEP provides sustainable, safe, and low-cost extraction of oil from soybeans, with simultaneous production of valuable co-products
Polysaccharide-hydrolyzing enzymes have a viscosity-reducing effect on the fermenting slurry, allowing higher glucan loading. These results indicate that enzymatic hydrolysis, when PCX enzymes were added during simultaneous saccharification and fermentation (SSF)
Integrated corn-insoluble fiber (IF) fermentation resulted in ~31% increase in ethanol production rate and a 5%
Summary
Enzyme-assisted aqueous extraction process (EAEP) is an environmentally friendly alternative to chemical (organic solvent such as hexane) or mechanical extraction of oil from soybeans [1,2,3].In comparison to conventional oil extraction methods, EAEP provides sustainable, safe, and low-cost extraction of oil from soybeans, with simultaneous production of valuable co-products. Enzyme-assisted aqueous extraction process (EAEP) is an environmentally friendly alternative to chemical (organic solvent such as hexane) or mechanical extraction of oil from soybeans [1,2,3]. In EAEP, soybeans are first mechanically treated to remove hulls, conditioned to set moisture, and extruded to increase surface area. The mixture of soybean extrudes and water is subjected to protease. Fermentation 2018, 4, 35 treatment, and the cream and co-products are separated by decanting followed by demulsification with the same protease to recover oil [2]. EAEP of soybeans results in ~97% of oil recovery, in addition to the production of large amounts of skim (protein-rich liquid fraction) and insoluble fiber (IF; carbohydrate-rich solid fraction). For EAEP of soybeans to be economically viable, the proper use of skim and IF must be found.
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